C8 - Rate of Reaction + Reversible reactions Flashcards
rate of reaction
-how fast reactant turn into products
Work out rate of reaction
-measure reactants being used up
-products formed
Method to measure rate of reaction
-measure starting mass + record as it decreases as gas is lost
-measure increasing gas volume (product) in gas syringe
-measure decreasing light passing through solution = precipitate appears (product)
mean rate of reaction
quantity of reactant used/time or quantity of product formed/time
Tangent in reaction graphs
-gradient = rate of reaction
-steeper gradient = fast reaction
Factors that affect rate
-temp
-SA
-concentration of solution
-pressure of gas
-catalysts
collision theory
-when particles of reactants come together
-must collide with enough energy to react
activation energy
-minimum energy necessary for particles to react with
How to increase rate in terms of particles
-increase frequency of collisions
-increase energy of collisions
Increased SA in rate of reaction
-more substance exposed to surface
-faster reaction
-increases frequency of collisions between particles
Effect of temp on rate of reaction
-particles have more energy
-for more collisions
-more chances to react
-increases rate and reduces time
Increased proportion of particles with more activation energy is
greater effect on rate than increased frequency of collisions
Effect of concentration on rate of reaction
-increasing = faster reaction
-more particles moving in same volume
=more collisions
Effect on increasing pressure on rate of reaction
-more collisions
-less space for particles to move
-increases rate
catalyst
a substance
-increases rate of reaction
-remains chemically unchanged
-does not get used up
Eg of catalysts
-iron to make ammonia
-platinum to make nitric acid
physical state of catalysts and why
-powder form
-better SA:V
-more effective
How do catalysts work
-provide an alternate reaction pathway to product
-lower activation energy is needed
-higher proportion of reactant particles have sufficient energy to react
Catalysts effect on frequency of collisions
-increases
-increases rate
Pros of catalysts
-cheaper than using extremely high temp/pressure
-save money
-help environment as no burning of fossil fuels
-sustainable = only a little is used
poisoned catalysts
-in chemical plants
-contaminated
-is prevented from working
reversible reaction
products can react to form reactants again
Litmus paper
-complex molecule
-Hlit
HLit
-H is for Hydrogen
-red
-add alkali = blue
HLit add an alkali
Lit- ion as H is lost
HLit can form
H+ and Lit -
water of crystallisation
-water contained within a crystal lattice
hydrated salt
-salt that contains water of crystallisation
anhydrous salt
-doesn’t contain water of crystallisation
Heating ammonium chloride
-thermal decomp
-forms ammonia gas and H
Reversible reaction of ammonium chloride
-when heated
-2 hot gases rise in test tube
-as they cool near top, they react
-gases re-form ammonium chloride
Energy in reversible reactions
-if a reaction is exothermic
-reversed reaction is endothermic
-will take in same amount of energy
-law of conservation of energy = not destroyed/created
stages of reversible reaction - stage 1
-reactants only at start of reaction
stages of reversible reaction - stage 2
-rate of forward reaction is greater than reverse reaction
stages of reversible reaction - stage 3
-rate of reverse increases as products build up
-rate of forward reaction decreases as reactants are used up
stages of reversible reaction - stage 4
rates even out
-they are the same
as concentration of products builds up..
rate of reverse reaction increases
-reactants re form
-forward reaction decreases
equilibrium
reactants make products at the same rate as products make reactants
-forward = backward
-no change in amount of products and reactants
dynamic equilibrium
-forward + reverse reactions continuously take place
Le chatelier’s principle
-lower concentration of reactants = decreases forward reaction
-changing conditions in a system of equilibrium will shift position of equilibrium to cancel out change
conditions in Le chatelier’s principle consist of
-pressure
-temp
-concentration
Why is Le chatelier’s principle important in industry
-chemists must find condition that produces most products in shortest amount of time
if the forward reactions produces more gas molecules ..
-increase in pressure decreases products formed
-decrease in pressure increases products
if forward reaction produces fewer gas molecules..
-increase in pressure increases products
-decrease in pressure decreases products
when there are equal numbers of molecules of gas on both sides of equation ..
-pressure cannot affect composition of equilibrium mixture
-but will speed up reaction in equal amounts
change in temp in a closed system
-more products
-less reactants
if forward reaction is exothermic
-increase in temp decreases products
-decrease in temp increases products
if forward reaction is endothermic
-increase in temp increases products
-decrease in temp decreases products
affect of increase in temp on equilibrium
-it shifts to reduce the temp
increasing temp favours which reaction
endothermic
decreasing temp favours which reaction
exothermic
